1. Field of the Invention
This invention relates to the preparation of substituted acid chlorides which are useful as intermediates for preparing pesticidally active compounds. In the novel process of this invention, excellent yields of pure substituted amino acid chlorides in a hydrocarbon solvent are obtained from the corresponding substituted amino acids.
2. Description of the Prior Art
U.S. Pat. No. 4,243,819 to Henrick et al describes substituted amino acid compounds suitable for use in the process of this invention. It also describes the use of the corresponding substituted amino acid chlorides as intermediates for preparing pesticidally active esters.
The chemical reaction of a carboxylic acid with phosgene in the presence of a tertiary amide to yield the corresponding acid chloride is a well known reaction. The use of N-methyl-2-pyrrolidone in the general reaction of organic acids to yield chlorides has been described in M-PYROL N-Methyl-2-Pyrrolidone Handbook, GAF Corporation (1972). More specific reaction details have been disclosed in other publications. Babad et al, Chemical Reviews Vol. 73 No. 1, 81-82 (1973); Ulrich et al, J.Org.Chem. 32 4052 (1967); German Pat. No. 1,167,819 (1964); German OLS No. 1,931,074 (1968) and British Pat. No. 1,159,266 (1969) describe the reaction of carboxylic acids or anhydrides with phosgene using a number of catalysts including tertiary amides to yield the corresponding acid chlorides. All of these references teach reaction temperatures approaching 100.degree. C. during an initial stage, and thereafter, increasing temperatures up to the reflex temperature (115.degree. to 150.degree. C.). In a final step, the solvent is removed by distillation at temperatures substantially above 100.degree. C. Elevated temperatures are required and minimal catalytic amounts of tertiary amides are used.
The prior art processes do not produce amino acid chlorides in high yield because the end products are unstable at high temperatures.